To a stirred solution of methyl 3-amino-2-thiophenecarboxylate (25.0 g, 159 mmol) in acetonitrile (325 mL) was added sequentially pyridine (15.5 mL) and trifluoroacetic anhydride (29.3 mL) at 0 °C. After 5 minutes of reaction, the reaction mixture was slowly warmed to room temperature and stirring was continued for 20 minutes. Subsequently, the reaction mixture was slowly poured into ice water (3.0 L) and stirred for 15 minutes to quench the reaction. The resulting precipitate was collected by filtration, washed with cold water and dried under vacuum to afford methyl 3-(2,2,2-trifluoroacetamido)-2-thiophenecarboxylate (37.3 g, 93% yield) as a pink solid. Its 1H NMR (300 MHz, DMSO-d6) data were as follows: δ 3.86 (3H, s), 7.72 (1H, d, J = 5.4 Hz), 8.03 (1H, d, J = 5.4 Hz), 11.17 (1H, br s).
